There are various applications where it is necessary to maintain a pressure on a fluid in a storage tank to maintain it in the liquid state for pumping purposes. The requirement becomes necessary when it is desirable to pump fluids which are volatile in nature within the ambient temperatures of the application. The fluid, which is contained in a tank, requires a certain minimum pressure to remain in a liquid state at a given temperature. The required pressure depends on the vapor pressure of the fluid which, in turn, is a function of temperature. Such gases as nitrogen can be supplied to the tank, under pressure, to maintain the given or required pressure of the fluid to maintain it in the liquid state.
There is a need for an improved pressure control system for such storage tanks which can be readily regulated as a function of the tank temperature. This invention is directed to solving such a need. Its advantage over a simplistic system of a constant supply regulator, which is set to a point above all vapor pressures of the fluid, is in pressurization gas consumption and potential contamination. In a system with a working fluid which is exposed to a wide range of ambient temperatures, such as in aircraft usage, and a fluid with a wide range of vapor pressures over those ambients, the required constant pressure would be significantly higher than that required for a majority of conditions. This higher than needed pressure can, dependent on the fluids involved, result in a higher absorption rate and potential unacceptable contamination of the pressurization gas into the liquid to be pumped. This simplistic approach also will require a larger volume of pressurization gas which would be disadvantageous in aircraft applications due to weight and size constraints.
An object, therefore, of the invention is to provide a new and improved control system for maintaining a fluid in a liquid state throughout a varying temperature range with minimized pressurizing gas consumption in a storage tank or the like.
In the exemplary embodiment of the invention, a supply of pressurization (gas) fluid, such as nitrogen, is provided under a pressure at least above that required to be maintained in the storage tank. Generally, conduit means establishes fluid communication between the working fluid supply and the storage tank. Supply regulator means are provided in the conduit means for maintaining a substantially constant pressure to the storage tank. Tank regulator means are provided in the conduit means between the supply regulator means and the storage tank for selectively admitting the substantially constant pressure to the storage tank. Control means are provided for selectively operating the tank regulator means in response to given conditions, such as the temperature condition, present in the storage tank.
As disclosed herein, the supply regulator means is a differential pressure valve. The tank regulator means includes a second differential pressure valve, along with a flapper valve for selectively admitting the constant pressure to the differential pressure valve. Control means, responsive to temperature conditions in the storage tank, are operatively connected to the flapper valve for controlling the tank regulator means to maintain a given pressure in the storage tank.
Other objects and features of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.